Choosing the image on which the baking goes
Here's the method I use: 


Create a new Texture in the UV/Image Editor and name it appropriately.
Create a new Image Texture node in the Node Editor (no connection to the tree) and select your created Image in the dropdown menu.
With this new texture node selected, go to yo Render Panel and bake your texture. 
Repeat from Step 1 for different Bake Types.